Busulfan produces efficient human cell engraftment in NOD/LtSz-Scid IL2Rgamma(null) mice

Xenografting immunodeficient mice after low-dose irradiation has been used as a surrogate human hematopoietic stem cell (HSC) assay; however, irradiation requires strict and meticulous animal support and can produce significant mortality rates, limiting the usefulness of this model. In this work, we examined the use of parenteral busulfan as an alternative conditioning agent. Busulfan led to dose-dependent human HSC engraftment in NOD/LtSz-scid/IL2Rgamma(null) mice, with marked improvement in survival rates. Terminally differentiated B and T lymphocytes made up most of the human CD45+ cells observed during the initial 5 weeks post-transplant when unselected cord blood (CB) products were infused, suggesting derivation from existing mature elements rather than HSCs. Beyond 5 weeks, CD34+-enriched products produced and sustained superior engraftment rates compared with unselected grafts (CB CD34+, 65.8% +/- 5.35%, vs. whole CB, 4.27% +/- 0.67%, at 24 weeks). CB CD34+ group achieved significantly higher levels of engraftment than mobilized CD34+-enriched peripheral blood (PB CD34+). At 8 weeks, all leukocyte subsets were detected, yet human red blood cells (RBCs) were not observed. Transfused human red cells persisted in the chimeric mice for up to 3 days; an accompanying rise in total bilirubin suggested hemolysis as a contributing factor to their clearance. Recipient mouse-derived human HSCs had the capacity to form erythroid colonies in vitro at various time points post-transplant in the presence of human transferrin (Tf). When human Tf was administered singly or in combination with anti-CD122 antibody and human cytokines, up to 0.1% human RBCs were detectable in the peripheral blood. This long evasive model should prove valuable for the study of human erythroid cells.

Hematopoietic stem cell transplantation prevents diabetes in NOD mice but does not contribute to significant islet cell regeneration once disease is established

The treatment of type I diabetes by islet cell transplantation, while promising, remains restricted due to the incomplete efficacy and toxicity associated with current immunosuppression, and by limited organ availability. Given reports suggesting bone marrow derived stem cell plasticity, we sought to determine whether such cells could give rise to pancreatic islet cells in vivo. In the context of autoimmune diabetes, we transplanted unfractionated bone marrow from beta-gal trangenic donor mice into NOD mice prior to, at, and two weeks beyond the onset of disease. Successful bone marrow engraftment before diabetes onset prevented disease in all mice and for 1 year after transplant. However, despite obtaining full hematopoietic engraftment in over 50 transplanted mice, only one mouse became insulin independent, and no beta-Gal positive islets were detected in any of the mice. To test whether tolerance to islets was achieved, we injected islets obtained from the same allogeneic donor strain as the hematopoietic cells into 4 transplant recipients, and 2 had a reversion of their diabetes. Thus allogeneic bone marrow transplantation prevents autoimmune diabetes and tolerizes the recipient to donor islet grants, even in diabetic animals, yet the capacity of bone marrow derived cells to differentiate into functional islet cells, at least without additional manipulation, is limited in our model.

High-efficiency transduction of rhesus hematopoietic repopulating cells by a modified HIV1-based lentiviral vector

Human immunodeficiency virus type 1 (HIV1) vectors poorly transduce rhesus hematopoietic cells due to species-specific restriction factors, including the tripartite motif-containing 5 isoformα (TRIM5α) which targets the HIV1 capsid. We previously developed a chimeric HIV1 (χHIV) vector system wherein the vector genome is packaged with the simian immunodeficiency virus (SIV) capsid for efficient transduction of both rhesus and human CD34(+) cells. To evaluate whether χHIV vectors could efficiently transduce rhesus hematopoietic repopulating cells, we performed a competitive repopulation assay in rhesus macaques, in which half of the CD34(+) cells were transduced with standard SIV vectors and the other half with χHIV vectors. As compared with SIV vectors, χHIV vectors achieved higher vector integration, and the transgene expression rates were two- to threefold higher in granulocytes and red blood cells and equivalent in lymphocytes and platelets for 2 years. A recipient of χHIV vector-only transduced cells reached up to 40% of transgene expression rates in granulocytes and lymphocytes and 20% in red blood cells. Similar to HIV1 and SIV vectors, χHIV vector frequently integrated into gene regions, especially into introns. In summary, our χHIV vector demonstrated efficient transduction for rhesus long-term repopulating cells, comparable with SIV vectors. This χHIV vector should allow preclinical testing of HIV1-based therapeutic vectors in large animal models.

5% dimethyl sulfoxide (DMSO) and pentastarch improves cryopreservation of cord blood cells over 10% DMSO

BACKGROUND

Cell number and viability are important in cord blood (CB) transplantation. While 10% dimethyl sulfoxide (DMSO) is the standard medium, adding a starch to freezing medium is increasingly utilized as a cytoprotectant for the thawing process. Similar to hetastarch, pentastarch has the advantages of faster renal clearance and less effect on the coagulation system.

STUDY DESIGN AND METHODS

We compared a lower DMSO concentration (5%) containing pentastarch with 10% DMSO and performed cell viability assay, colony-forming units (CFUs), and transplantation of CB cells in NOD/SCID IL2Rγ(null) mice.

RESULTS

CB cells in 5% DMSO/pentastarch had similar CD34+, CD3+, and CD19+ cell percentages after thawing as fresh CB cells. CB cells in 5% DMSO/pentastarch had higher viability (83.3±9.23%) than those frozen in 10% DMSO (75.3±11.0%, p<0.05). We monitored cell viability postthaw every 30 minutes. The mean loss in the first 30 minutes was less in the 5% DMSO/pentastarch group. At the end of 3 hours, the viability decreased by a mean of 7.75% for the 5% DMSO/pentastarch and 17.5% for the 10% DMSO groups. CFUs were similar between the two cryopreserved groups. Frozen CB cells engrafted equally well in IL2Rγ(null) mice compared to fresh CB cells up to 24 weeks, and CB cells frozen in 5% DMSO/pentastarch engrafted better than those in 10% DMSO.

CONCLUSION

Our data indicate that the lower DMSO concentration with pentastarch represents an improvement in the CB cryopreservation process and could have wider clinical application as an alternate freezing medium over 10% DMSO.

Low-dose parenteral busulfan provides an extended window for the infusion of hematopoietic stem cells in murine hosts

OBJECTIVE

Myeloablative total body irradiation (TBI) in the setting of autologous transplantation of genetically modified hematopoietic stem cells (HSC) is associated with substantial toxicity. Nonmyeloablative doses of TBI are less toxic, but result in low-level engraftment of genetically modified HSCs. As an alternative to TBI, escalating doses of parenteral busulfan were tested for their hematologic toxicity, their ability to promote donor leukocyte engraftment, and the time window for such engraftment.

MATERIALS AND METHODS

Hematologic toxicity of busulfan was assessed in C57BL6 mice after single nonmyeloablative doses of intraperitoneal busulfan ranging from 1 to 40 mg/kg by serial complete blood counts monitored up to 40 days. The level of donor engraftment attainable after nonmyeloablative busulfan was determined by infusion of 20 million congenic murine bone marrow nucleated cells (BMNC) following 5 to 40 mg/kg of busulfan. To determine the effects of delayed HSC infusions, BMNCs were infused 1, 10, 15, and 20 days after a single dose of 10 mg/kg of busulfan.

RESULTS

Busulfan doses from 1 to 40 mg/kg produced hematologic toxicity that was most pronounced in the 2nd to 3rd week. In transplantation experiments, dose-dependent donor leukocyte engraftment was attained with levels >70% after only 20 mg/kg of busulfan. Similar levels of engraftment were achieved even when infusion of BMNCs was delayed up to 20 days after busulfan injection.

CONCLUSION

Nonmyeloablative parenteral busulfan produced transient myelosuppressive effects, clinically relevant levels of engraftment, and an extended time window for HSC infusion in murine hosts.

Long-term vector integration site analysis following retroviral mediated gene transfer to hematopoietic stem cells for the treatment of HIV infection

We previously reported the efficacy of nonmyeloablative allogeneic transplantation in 2 HIV positive recipients, one of whom received retrovirus transduced hematopoietic stem cells to confer resistance to HIV. Here we report an assessment of retroviral integration sites (RISs) recovered out to 3 years post-transplantation. We identified 213 unique RISs from the patient's peripheral blood samples by linear amplification-mediated PCR (LAM-PCR). While vector integration patterns were similar to that previously reported, only 3.76% of RISs were common among early (up to 3 months) and late samples (beyond 1 year). Additionally, common integration sites were enriched among late samples (14.9% vs. 36.8%, respectively). Three RISs were found near or within known oncogenes, but 2 were limited to early timepoints. Interestingly, an integration site near the MDS1 gene was detected in long-term follow-up samples; however, the overall contribution of MDS1 integrated clone remained stably low during follow-up.

Cloning and Functional Analysis of the Rhesus Macaque ABCG2 Gene

Hematopoietic cells can be highly enriched for repopulating ability based upon the efflux of the fluorescent Hoechst 33342 dye by sorting for SP (side population) cells, a phenotype attributed to expression of ABCG2, a member of the ABC transporter superfamily. Intriguingly, murine studies suggest that forced ABCG2 expression prevents hematopoietic differentiation. We cloned the full-length rhesus ABCG2 and introduced it into a retroviral vector. ABCG2-transduced human peripheral blood progenitor cells (PBPCs) acquired the SP phenotype but showed significantly reduced growth compared with control. Two rhesus macaques received autologous PBPCs split for transduction with the ABCG2 or control vectors. Marking levels were similar between fractions with no discrepancy between bone marrow and peripheral blood marking. Analysis for the SP phenotype among bone marrow and mature blood populations confirmed ABCG2 expression at levels predicted by vector copy number long term, demonstrating no block to differentiation in the large animal. In vitro studies showed selective protection against mitoxantrone among ABCG2-transduced rhesus PBPCs. Our results confirm the existence of rhesus ABCG2, establish its importance in conferring the SP phenotype, suggest no detrimental effect of its overexpression upon differentiation in vivo, and imply a potential role for its overexpression as an in vivo selection strategy for gene therapy applications.

The assessment of human erythroid output in NOD/SCID mice reconstituted with human hematopoietic stem cells

The third-generation NOD/LtSz-scid/IL2Rγ(null) (NOD/SCID IL2Rγ(null)) mouse represents a significantly improved xenograft model allowing high levels of human leukocyte engraftment over extended follow up. One remaining limitation of this mouse model, however, is the low level of circulating human erythrocytes. We established a practical ex vivo erythroid culture system of xenograft marrow progenitors to enrich for human erythroid progeny. At various time points after transplant, erythroid cells were easily assayed after 17 days of ex vivo culture of xenograft marrow, with nearly all nucleated cells of human origin and approximately 60% human GPA or CD71 positive. We then transplanted cord blood CD34(+) cells marked with a lentiviral vector encoding green fluorescent protein (GFP). Three months later, ex vivo culture of xenograft marrow progenitors showed 41.3% of the cultured erythroid cells were positive for GFP and human CD71, and 56.2% were positive for GFP and human GPA, similar to that of circulating leukocytes at the same time point. Next, G-CSF mobilized peripheral blood CD34(+) cells from a sickle cell trait subject were infused in this mouse model to determine if the hemoglobin pattern could be modeled. CD34(+) cells from the sickle cell trait subject engrafted equally compared to CD34(+) cells from normal subjects, establishing the sickle cell trait phenotype. Lastly, a comparison of adult-derived peripheral blood CD34(+) cells and cord blood-derived CD34(+) cells xenografted mice was made, and long term follow-up demonstrated a recapitulation of the fetal to adult hemoglobin switch. This approach should prove a useful tool for testing strategies for genetic manipulation of erythroid progeny and the study of hemoglobin switching.

Transient in vivo beta-globin production after lentiviral gene transfer to hematopoietic stem cells in the nonhuman primate

Inherited disorders of globin synthesis remain desirable targets for hematopoietic stem cell (HSC)-based therapies. Gene transfer using retroviral vectors offers an alternative to allogeneic HSC transplantation by the permanent integration of potentially therapeutic genes into primary autologous HSCs. Although proof of principle has been demonstrated in humans, this approach has been met by formidable obstacles, and large-animal models have become increasingly important for the preclinical development of gene addition strategies. Here we report lentiviral gene transfer of the human beta-globin gene under the control of the globin promoter and large fragments of the globin locus control region (LCR) in the nonhuman primate. Using an HIV-1, vesicular stomatitis virus glycoprotein G (VSV-G)-pseudotyped vector, modified to overcome a species-specific restriction to HIV-1, gene transfer to colony-forming units (CFU) derived from mobilized peripheral blood (PB) rhesus CD34+ cells was 84.4 +/- 2.33%. Erythroid cells derived from transduced rhesus CD34+ cells expressed human beta-globin at high levels as assessed by flow cytometry with a human beta-globin-specific antibody. Two rhesus macaques (RQ3586 and RQ3583) were transplanted with mobilized PB CD34+ cells transduced with our modified HIV vector at a multiplicity of infection of 80. High gene transfer rates to CFUs were achieved in vitro (RQ3586, 87.5%; RQ3583, 83.3%), with efficient human beta-globin expression among erythroid progeny generated in vitro. Early posttransplantation, gene transfer rates of 5% or higher were detectable and confirmed by genomic Southern blotting, with equivalent-level human beta-globin expression detected by flow cytometry. Long-term gene marking levels among mononuclear cells and granulocytes assessed by quantitative polymerase chain reaction gradually decreased to about 0.001% at 2 years, likely due to additional HIV-1 restrictive elements in the rhesus macaque. No evidence of clonal hematopoiesis has occurred in our animals in up to 2 years. Current efforts are aimed at developing a lentiviral vector capable of efficiently transducing both human and rhesus HSCs to allow preclinical modeling of globin gene transfer.

Addition of rapamycin to anti-CD3 antibody improves long-term glycaemia control in diabetic NOD mice

Aims/Hypothesis

Non-Fc-binding Anti CD3 antibody has proven successful in reverting diabetes in the non-obese diabetes mouse model of type 1 diabetes and limited efficacy has been observed in human clinical trials. We hypothesized that addition of rapamycin, an mTOR inhibitor capable of inducing operational tolerance in allogeneic bone marrow transplantation, would result in improved diabetes reversal rates and overall glycemia.

Methods

Seventy hyperglycemic non-obese diabetic mice were randomized to either a single injection of anti CD3 alone or a single injection of anti CD3 followed by 14 days of intra-peritoneal rapamycin. Mice were monitored for hyperglycemia and metabolic control.

Results

Mice treated with the combination of anti CD3 and rapamycin had similar rates of diabetes reversal compared to anti CD3 alone (25/35 vs. 22/35). Mice treated with anti CD3 plus rapamycin had a significant improvement in glycemia control as exhibited by lower blood glucose levels in response to an intra-peritoneal glucose challenge; average peak blood glucose levels 30 min post intra-peritoneal injection of 2 gr/kg glucose were 6.9 mmol/L in the anti CD3 plus rapamycin group vs. 10 mmo/L in the anti CD3 alone (P<0.05).

Conclusions/Interpretation

The addition of rapamycin to anti CD3 results in significant improvement in glycaemia control in diabetic NOD mice.

Nonmyeloablative conditioning employing busulfan and sirolimus permits donor-dominant stable chimerism in a murine model of haploidentical allogeneic stem cell transplantation (P2192)

Allogeneic stem cell transplant (SCT) is a potentially curative option for many hematologic diseases, yet donor availability remains a challenge, and haploidentical SCT is associated with a higher risk of rejection. We successfully translated a model based on total-body irradiation (TBI) with to humans; however, TBI involves toxicities and risk of malignant side-effects, and we hypothesize that busulfan may be a superior alternative in some settings. G-CSF-mobilized F1/J (C57BL/6-BALB/c hybrid) splenocytes were injected into C57BL/6 hosts who had received 10-30mg/kg IP busulfan the previous day. All recipients received 31 days of 3mg/kg IP sirolimus beginning the day before transplant. No GvHD was observed and counts recovered by week 8 in all groups. Mice conditioned with 30mg/kg busulfan displayed remarkably high donor chimerism (&gt;90%), which was significantly higher than 300cGy TBI-conditioned control mice (64-86%) across all timepoints. Mice receiving 30mg/kg or 20mg/kg busulfan maintained stable chimerism for over 18 months. Mice conditioned with 10mg/kg busulfan showed only transient chimerism through 4 weeks. Proliferation of CD4+ cells in response to donor increases with decreasing busulfan, and mice receiving 30mg/kg responded more strongly than mice receiving TBI. A memory effect was observed in mice that received 10mg/kg busulfan and lost their grafts. Notably, a slightly higher incidence of host-derived Tregs in mice was also observed after graft rejection.

Recipient Cells Are the Source of Hematologic Malignancies After Graft Failure and Mixed Chimerism in Adults with SCD

Non-myeloablative hematopoietic cell transplantation (HCT) is a curative option for individuals with sickle cell disease (SCD). Our traditional goal with this approach has been to achieve a state of mixed donor/recipient chimerism. Recently, we reported an increased risk of hematologic malignancies (HMs) in adults with SCD following graft failure or mixed chimerism. To evaluate the origin of HMs, we performed chimerism analyses of 5 patients with SCD who developed HMs after non-myeloablative HCT. DNA was extracted from sorted peripheral blood or bone marrow cells representing mature cell lineages or leukemic blasts and subjected to chimerism analysis by PCR amplification of polymorphic short tandem repeats. Unlike mature cell lineages in patients with mixed chimerism, which still showed a donor-derived fraction of cells, leukemic blast cells were found to be 99-100% recipient-derived in all patients. Non-myeloablative conditioning allows for the survival of patients' cells that might harbor pre-leukemic clones that possess the capacity to evolve under genotoxic or environmental stress into malignancies; therefore, we have modified our HCT protocols with the goal of full donor chimerism to mitigate the risk of HM development.

Two Nonmyeloablative HLA-Matched Related Donor Allogeneic Hematopoietic Cell Transplantation Regimens in Patients with Severe Sickle Cell Disease

Nonmyeloablative (NMA) conditioning is being used increasingly with success in matched related donor (MRD) and alternative donor allogeneic hematopoietic cell transplantation (allo-HCT) in individuals with sickle cell disease (SCD). Advantages include decrease toxicity and applicability in patients otherwise unable to tolerate conditioning regimens due to end-organ damage or age. We aimed to add to published data outcomes of two similar NMA conditioning protocols, termed Protocol 1 (ClinicalTrials.gov ID NCT00061568) and Protocol 2 (ClinicalTrials.gov ID: NCT02105766)) in mainly adult patients with SCD to evaluate the safety, toxicity, and success of these regimens in individuals at high-risk for poor transplantation-related outcomes. We also evaluated the tolerability and outcomes of Protocol 2, which included preconditioning immunodepletion, in patients at even higher risk of T cell-mediated rejection or plasma/B cell-mediated anti-donor erythrocyte antibody production-the latter due to ABO incompatibility or recipient RBC alloimmunization to a donor antigen. Finally, we evaluated the incidence and trajectory of mixed donor myeloid chimerism over time following allo-HCT. In this retrospective analysis of the 2 prospective phase 2 NMA transplant protocols, 91 individuals with SCD or transfusion-dependent β-thalassemia underwent MRD allo-HCT at the National Heart, Lung, and Blood Institute; regimens contained alemtuzumab, low-dose radiation, and sirolimus for graft-versus-host disease (GVHD) prophylaxis with or without preconditioning immunodepletion with pentostatin and oral cyclophosphamide (Protocol 2). In the total cohort of 91 transplantation recipients, outcomes were favorable with timely neutrophil and platelet engraftment (median, 21 days [range, 7 to 67 days] and 21 days [range, 10 to 112 days], respectively), minimal high-grade acute GVHD and no chronic GVHD, overall survival of 90%, sickle-free survival of 85%, and mixed donor myeloid chimerism in 43% at a median follow up of 7.3 years (range, 0.8 to 20 years). Most patients with mixed myeloid chimerism at 2-years post-HCT remained stable in their values. In analyzing each protocol separately, outcomes were comparable except for higher cytomegalovirus reactivation necessitating treatment in Protocol 2 without an associated increase in graft failure. In the combined cohort, graft failure occurred in 11 patients, and hematologic malignancy or abnormal cytogenetics on bone marrow evaluation developed in 7 patients. In a subanalysis of factors that may implicate transplantation outcomes, the number of RBC units transfused post-HCT was significantly higher in recipients with pre-HCT history of alloimmunization to donor RBC antigens. There was no difference in the number of RBC units transfused, duration of transfusion, or red cell engraftment in those with major ABO incompatibility; preconditioning immunodepletion and pretreatment with rituximab likely were helpful. Both NMA allo-HCT protocols were successful in achieving adequate engraftment and sickle-free survival with minimal toxicity, including in individuals with mixed donor myeloid chimerism. The addition of preconditioning immunodepletion was well-tolerated and reduced the rate of graft failure in high-risk recipients.

Sirolimus, Post–Transplant Cyclophosphamide, and CTLA4-Ig Maintain Stable Mixed Chimerism In a Mismatched Murine Model

Hematopoietic stem cell transplantation (HSCT) is the only curative option for patients with sickle cell disease (SCD). We sought to extend our haploidentical HSCT regimen with nonmyeloablative conditioning. The objective of our study was to assess the ability of the immunosuppressive agent CTLA4-Ig to induce mixed chimerism in the haploidentical HSCT setting when combined with sirolimus, post-transplant cyclophosphamide (PT-Cy), or both.

We used a mismatched mouse model with BALB/c donors and C57BL/6 recipients. Recipient mice received 200 cGy TBI on day of the transplant and were conditioned with or without sirolimus, PT-Cy, and/or CTLA4-Ig.

Our data show that when CTLA4-Ig alone or CTLA4-Ig/PT-Cy are given, donor cells are not detected. However, mixed chimerism is maintained in mice who received either sirolimus/PT-Cy or sirolimus/PT-Cy given together with CTLA4-Ig over 60 days. Additionally our data indicate a significant increase in recovery of donor cells within CD8 T-cell, CD19 B-cell, and CD11b myeloid cell populations in groups conditioned with sirolimus/PT-Cy, or sirolimus/PT-Cy/CTLA4-Ig as compared to groups conditioned with CTLA4-Ig (p=0.003; p=0.002; p=0.049) alone or CTLA4-Ig/PT-Cy (p=0.001; p&lt;0.0001; p=0.001) at 30 days, respectively.

These data demonstrate that sirolimus in combination with PT-Cy and CTLA4-Ig is synergistic in an MHC-mismatched mouse model. The novel tri-drug group establishes mixed chimerism while conditioning with CTLA4-Ig alone or CTLA4-Ig/PT-Cy does not. The data also identify induction of stable mixed chimerism in specific cellular subpopulations within the sirolimus/PT-Cy and sirolimus/PT-Cy/CTLA4-Ig groups, indicating that these cells may play an important role in HCST.